The invention relates to a tube bundle heat exchanger having tubes that are held at each side in tube plates or oval tube collecting tube plates and are connected to these in each case by means of a weld seam, for cooling, by means of a cooling medium surrounding the tubes, a hot gas flow that is directed through the tubes, exhibiting at least one gas inlet chamber, from which the hot gas flow is directed into the individual tubes and which is delimited at one side by the inlet-side tube plate or oval tube collecting tube plate, and at least one gas outlet chamber in which the gas flow directed through the tubes is collected and discharged and which is delimited on one side by the outlet-side tube plate or oval tube collecting tube plate.
As a rule, for cooling gases in many materials processing installations, such as, for example, gasification installations, thermal and catalytic splitting installations, steam reforming installations, etc., heat exchangers, in particular, tube bundle heat exchangers (coolers), are used, into which the gases to be cooled flow through straight tubes and thereby give off the latent heat of the hot gas through the tube wall to the medium surrounding the tubes, in particular, the cooling medium. It is characteristic of such heat exchangers that the gases to be cooled are often under high pressure and at a high temperature and enter the straight tubes of the heat exchanger at high speed. As a result, at the tube inlet or the first section of the tube, a high heat flow density is achieved, which causes both a high temperature as well as high thermal stress in the tubes of the heat exchanger or in the tube plate—tube connection.
In state of the art heat exchangers, the tubes that conduct the gas are welded into the tube plates, whereby the weld seam between tube plate and tube is applied either at the outer or inner wall of the tube plate or inside the tube plate opening. For example, printed document DE 37 15 713 C2 exhibits a welded connection of the tube or tubes with the outer wall of the tube plate or the oval tube collecting tube plate.
The disadvantage of this known design consists in the fact that the gas-facing contour or surface of the transition from the tube to the tube plate or the oval tube collecting tube plate does not exhibit an exactly aerodynamic form. As a rule, the use of an inserted sleeve is undesirable for a number of different reasons, among them a narrowing of the gas-side cross section as well as an inadequate cooling of the sleeve. In addition, a gap can appear on the cooling medium side of the tube plates—tube connection, leading to water-side corrosion, or the tube plates—tube connection can exhibit a corner in which an unwanted stress concentration occurs.
Through document EP 1 154 143 A1, a cooler has become known in whose heat exchanger tubes, which lie between an inlet-side tube plate and an outlet-side tube plate, an exhaust gas is cooled by cooling water. Through the cooling of the exhaust gas, a condensate that exhibits a corrosive component is created, which causes corrosion at the connection of the particular tube with the outlet-side tube plate. As a result of this corrosion, a leak of the cooling water occurs at this connection, which leads to damage of the downstream machine. To prevent the leak, it is suggested that the connection of the particular tube with the outlet-side tube plate be designed in such a way that the tube is placed through the tube plate in a conical manner and the conical part of the tube is completely laser welded to the tube plate in order to achieve a deep-reaching welded connection.